Method of making contacts



Feb. 18, 1969 w. RENZ METHOD OF MAKING CONTACTS Filed Jan. 6, 1964 Sheet of 2 J8e 58d i as - lE i PRIOR ART W 1 m & \Q

" PRIOR ART INVENTOR Wilhelm Pen;

PRIOR ART Feb. 18, I969 RENZ 3,427,716

METHOD OF MAKING CONTACTS Filed Jan. 6, 1964 Sheet Z of2 Fly". 5

INVENI OR Wilhelm Renz BY r RN United States Patent O 3,427,716 METHOD OF MAKING CONTACTS Wilhelm Renz, Pforzheim, Germany, assignor to Firma Renz, Wacker & Co. Ohg., Kettens und Machinenfabrik, Calmbach (Enz), Germany Filed Jan. 6, 1964, Ser. No. 335,886 Claims priority, applicationzgermany, Jan. 9, 1963,

US. Cl. 29-630 Int. Cl. H01r 9/04; B21g 3/12 ABSTRACT OF THE DISCLOSURE 1 Claim A hot welded bimetallic electrical contact without folds mer blows to avoid the formation of folds in the upset head of the workpiece.

This invention relates to a method and apparatus for making upset parts without forming folded portions and is particularly directed to the making of electrical contact parts such as hot-welded bimetallic contact parts on a rotatable table rivet upsetting machine.

When bimetal contact parts are made by cold press Welding, the high pressure causes a spreading of the facing surfaces of the two metal components, such as copper and silver. In cold press Welding, more material of limited availability is needed for the formation of a large contact head. Approximately the same amount of copper and silver must be used in the cold press welding. These pieces of metal can only be of a length such that they will not bend during the forming of a contact part. Also, in cold press welding, a better weld is obtained as the metal layers are thinner. However, as more copper is needed for feeding the copper into the press, a fold is formed in the metal which can extend into the stern of the contact. A cold press bimetallic contact part without a folded portion can only be obtained in contacts so small that they are never used in practice, as, for example, a contact having a head up to about 0.6 mm.

Ordinarily a hot press bimetallic contact without a compressed fold can be obtained only with a head having a height up to about 1 mm.

These compressed folds in the contact head have a detrimental effect when two electrical contacts are closed. The electrical resistance at the fold is larger and this point becomes hot. Because two opposed contacts constantly strike at the center of the contact surfaces, the folded portions separate in the course of time. This disadvantage occurs especially in high voltage switches.

The object of this invention is to produce a bimetallic electrical contact without having folded portions.

In general, this object is obtained by forming the contact head by means of many rapidly applied hammer blows while the material is being fed in the machine. It is possible to manufacture large contacts and especially hotwelded bimetallic contacts without the objectionable folded portions.

The apparatus of this invention has a smoothly sloped cam for feeding the material in the riveting machine and a serrated cam which controls the rate at which the hammer blows are applied to the workpiece. The two cams are such that the smooth cam has a slope which increases as the slope of the serrated cam decreases. The serrations in the serrated cam are more closely spaced from the beginning to the end of the cam slope.

The means by which the objects of the invention are obtained are described more fully with reference to the accompanying drawings in which:

FIGURE 1 is a side view, partly in section, of a portion of the riveting machine of the prior art;

FIGURE 2 is an enlarged cross-sectional view through a partially formed hot press welded bimetallic contact formed in the machine of FIGURE 1 and having folded portions;

FIGURE 3 is a view similar to FIGURE 2, but showing the finished bimetallic contact;

FIGURE 4 is a view similar to a portion of FIGURE 1 showing the improvement of this invention;

FIGURE 5 is an enlarged cross-sectional view of a hot press welded bimetallic contact as initially formed by this invention; and

FIGURE 6 is a view similar to FIGURE 5 showing the finished bimetallic contact of this invention.

In the prior art machine of FIGURE 1, the rotatable table 10 of the rivet machine has a plurality of openings 12 adapted to receive the bimetallic contact elements, such as a length of copper wire 14 and a silver piece 16. The table revolves to bring the pieces to the pressing station. Here a plunger 18 is moved upwardly into the hole to push the workpiece composed of the copper wire 14 and the silver piece 16 upwardly. This upward movement is caused by a wedge 20 moved by a wedge plate 24. The movement is controlled by means of a cam 26 which has a stepped cam slope composed of surface segments 26a-d. Cam follower 28 is on one end of a lever 30 pivotally mounted on a shaft 32 while the other end of the lever engages the wedge plate 24 by means of an adjustable bolt 34. As the cam turns, the cam slopes 26a and b will cause the plunger 18 to rise in a series of steps.

As the workpiece rises, it is struck by hammer 36 which is actuated by a cam 38 having cam slopes 38a-e. Thus, as the workpiece rises through the hole in the table, it is struck by the hammer as determined by the cam follower 40 riding on theslopes 38ae, inclusive. Because of the lengths of these slopes, only a few hammer blows are applied to the workpiece. This results in that folds 42 in the silver piece and folds 44 in the copper wire are formed during the upsetting of the workpiece, and these folds are carried into the finished workpiece, as shown in FIGURES 2 and 3.

In this invention, the stepped slope cam 26 of the prior art is replaced by a cam 50 having a smoothly curved cam slope 52. Consequently, the workpiece is pushed upwardly continuously rather than in steps. Also, the hammer cam is replaced by a serrated cam 54 having a serrated slope 56. In general, the serrations are approximately about 0.1 mm. from point to point, about twenty-four serrations being used. The first four serrations 56a are preferably longer than 0.1 mm. Thus, as the workpiece rises, it is struck rapidly by the hammer. As shown in FIGURES 5 and 6, the result is that the workpiece does not have any folded portions, but obtains a roughened surface 58 which disappears in the finished bimetallic contact shown in FIGURE 6. The process is relatively continuous as compared to the step by step lifting and striking the workpiece used by the prior art.

Having now described the means by which the objects of the invention are obtained.

I claim:

1. In a method of making hot welded bimetallic contacts without folds on a rotatable table rivet upsetting machine in which the workpiece is fed upwardly through a hole in the table while being upset by about twelve strokes of an impact tool during a unit of time, the improvement comprising substantially continuously and uninterruptedly feeding the workpiece upwardly while simultaneously rapidly striking and upsetting the workpiece with from about twenty-four hammer blows during the same unit of time to avoid the formation of folds in the upset head of the workpiece.

References Cited UNITED STATES PATENTS 3,151,385 10/1964 Gwyn 29630 3,279,505 10/1966 Renz et al 29-155.55

FOREIGN PATENTS 8/1962 Germany.

OTHER REFERENCES Fiat Report 785: pp. 13 and 14, copy in 29-155.55C, group 323, pub. February 1946.

What Designers Should Know About Cold Welding: Machinery, April 1967 issue, p. 195, copy in group 320, class 10-27.

JOHN F. CAMPBELL, Primary Examiner.

R. W. CHURCH, Assistant Examiner.

. US. Cl. X.R. 

